1. Field of the Invention
The present invention relates to an image sensor having a light receiving unit for converting light into electric charge and a scanning circuit for scanning light receiving pixels and reading electric charge generated at the light receiving unit as signal, particularly to an image sensor of a laminated layer type in which a light receiving unit is laminated on a scanning circuit.
Further, the present invention relates to an active matrix type display device integrated with an image sensor and a display matrix of a laminated layer type.
2. Description of Related Art
An optical sensor is widely used as a sensor for converting light into electric signal. For example, an optical sensor is widely used as an image sensor for a facsimile, a copier, a video camera, a digital still camera or the like.
To meet request of multimedia, high density formation of pixels of an image sensor has been rapidly progressed. For example, in respect of standard of pixels of a digital still camera, the high speed formation is promoted from VGA (Video Graphics Array) (640×480=310,000 pixels) to SVGA (Super VGA) or XGA (Extended Video Graphics Array), further to SXGA (Super XGA) (1280×1024=1,310,000 pixels).
Further, to meet request of small-sized formation and low cost formation of a multimedia tool such as a digital still camera or the like, an optical system has been downsized year by year from ⅔ inch to ½ inch to ⅓ inch and ¼ inch.
In this way, an image sensor which is a small light receiving cell having excellent conversion efficiency has been requested to realize high density formation of pixels and small-sized formation of an optical system. To satisfy the request, for example, to promote an aperture ratio, there has been proposed an image sensor of a laminated layer type in which a scanning circuit for reading electric charge generated at a light receiving unit as signal and the light receiving unit (photo diode unit) are laminated.
In recent years, a technology of fabricating TFT (Thin Film Transistor) using polycrystal silicon which is referred to as polysilicon TFT has been studied intensively. As a result, it becomes possible to fabricate a drive circuit of a shift register circuit or the like by a polysilicon TFT and there has been reduced into practice a liquid crystal panel of an active matrix type in which a display matrix and a peripheral drive circuit for driving the display matrix are integrated on the same substrate. Thereby, low cost formation, small-sized formation and light-weighted formation of a liquid crystal panel have been achieved and therefore, the liquid crystal panel has been used in display units of various information devices and portable devices of a personal computer, a portable telephone, a video camera, a digital camera and so on.
There has been currently reduced into practice a small-sized portable information processing terminal device which is more excellent than a notebook type personal computer in portability, inexpensive and of a pocket size and an active matrix type liquid crystal panel is used for a display unit thereof. According to such an information processing terminal device, data can be inputted from the display unit by a touch pen system, in order to input data/graphic information on paper or image information, a peripheral device of a scanner, a digital camera or the like is needed. Therefore, the portability of the information processing terminal device is deteriorated. Further, economic burden is imposed on a user to purchase the peripheral device.
Further, an active matrix type display device is also used in a display unit for a TV conference system, a TV telephone, a terminal for internet or the like. According to the system or the terminal, a camera for taking picture of a dialogue partner or a user is provided and a display unit and a camera unit are individually fabricated into modules.